The present invention relates to a magnetic recording/reproducing apparatus and, more particularly, to a magnetic recording/reproducing apparatus with a tape loading system wherein a magnetic recording tape is pulled out from a cassette and is wound around a rotary head cylinder.
Video tape recorders are well known as magnetic recording/reproducing apparatuses with the above-mentioned tape loading system. Several types of tape loading systems are known. Among them are the parallel loading system (sometimes called M type system or VHS system) and the U-type loading system (sometimes called .DELTA. system). In any known system, a magnetic recording tape is pulled from the cassette and wound around a rotary head cylinder through a predetermined angle. After that, the rotary head cylinder is rotated and the tape is run. And, at that time, the helical scanning of the tape is conducted, whereby signals are recorded on or reproduced from the the magnetic recording tape.
FIGS. 1 to 3 are schematic views showing a conventional tape loading system for use in a video tape recorder. This is a parallel loading system. As shown in FIG. 1, a rotary head cylinder 1 is rotatably disposed on the chassis of a video tape recorder. Two recording/playback heads (not shown) are spaced apart by an angular interval of 180.degree. along the circumference of the rotary head cylinder 1. The cylinder 1 is inclined at a predetermined angle to the direction of arrow S where is a point on the peripheral surface of the rotary head cylinder 1 near its tape entrance point. It is rotated by a motor (not shown) at a predetermined speed in the recording or playback mode. As shown in FIG. 3, a loading post 2 and a tilt post 3 are mounted on a loading arm 4. Likewise, a loading post 2' and a tilt post 3' are mounted on a loading arm 4'. The tilt posts 3, 3' are inclined in the same direction. The posts 2 and 3 form a loading member, and the posts 2' and 3' also form a loading member. These loading members are positioned in the opening of the cassette case, as indicated by broken lines in FIG. 1, before a magnetic recording tape 15 stored in a cassette 16 is wound around the cylinder 1. They are moved by the loading arms 4 and 4' in the directions indicated by arrows A, thereby pulling the tape 15 out of the cassette 16 and winding it around the cylinder 1. Finally they are located symmetrical with respect to the cylinder 1, as indicated by solid lines in FIG. 1.
Referring to FIG. 1, reference numerals 6 and 7 respectively denote impedance rollers and they are used to ensure a stable traveling of the tape 15. Hence, the free vibration of the tape 15 is suppressed so as to decrease jitter components. An audio control signal recording/reproducing head 8, a full-width erase head 9, a tension post 10, a pinch roller 11, and a capstan 12 are further provided. The capstan 12 cooperates with the pinch roller 11 to cause the tape 15 to travel at a predetermined speed.
When the loading post 2 and tilt post 3 and the loading post 2' and tilt post 3' are moved substantially parallel, in the directions of arrows A, the tape 15 which is wound around the supply reel 13 and a take-up reel 14 of the cassette 16 is automatically pulled out and wound around the rotary head cylinder 1 through an angle of .beta. as shown in FIG. 2. In the video tape recorder using the parallel loading system, since the tape 15 can be wound around the cylinder 1 when the posts 2, 3, 2', 3' are so moved as shown by arrows A in FIG. 1, the loading mechanism comprised of these posts 2, 2', 3, 3' needs a considerably small space. Futhermore, the upper edge of the tape 15 at the tilt post 3 located on the tape entrance side, the upper edge of the tape 15 on that point of the cylinder 1 which is at an angular distance of about 90.degree. from the tilt post 3, and the upper edge of the tape 15 at the tilt post 3' located on the tape exit side are set at substantially the same height "H" from the surface 17 of the chassis. Therefore, the video tape recorder, which has the parallel loading system, is smaller, particulary thinner, than the video tape recorder having an U-type loading system, as well known in this field of art.
In recent years it is much demanded that the video tape recorder be made portable. The manufacturers have long been making great efforts to provide a portable video tape recorder. Most of the existing video tape recorders for household use employ a tape reel having a width of 12.7 mm. The cassette containing two reels of this size hinders the miniaturization of video tape recorders. At present, the manufacturers are trying to develop a video tape recorder which uses a magnetic recording tape having a width of 8 mm (hereinafter referred to as "an 8 mm VTR"). Some prototype 8 mm VTRs have already been produced.
Of these 8 mm VTRs, the type which uses the so-called parallel loading system is particularly advantageous from the standpoint of reducing the planar size and thickness of a VTR. Nonetheless, whether the magnetic recording tape has a width of 12.7 mm or 8 mm, the parallel loading system requires two tilt posts 3 and 3' to guide a magnetic recording tape 15 over the outer peripheral surface of a rotary head cylinder and also to smoothly remove the tape 15 therefrom. (In contrast, the U-type loading system requires only one tilt post on the tape entrance side to smoothly guide and remove the tape, regardless of the width of the tape, 12.7 mm or 8 mm.) To make the matter worse, the tilt posts 3, 3' are not allowed to revolve. Should they revolve by themselves, the tape 15, which slidably contacts those posts, would be moved along in the longitudinal direction of these posts 3, 3'. In this event, the upper edge of the tape 15 contacting the posts 3, 3' would have a greater height from the surface 17 than the aforementioned height H. This would make it impossible to retain the thinness of the parallel loading system. Not only the tilt posts 3, 3' are set very close to the tape inlet point "m" and tape outlet point "n" on the peripheral surface of the rotary head cylinder 1. Also, the sum of the angles through which the tape 15 is wrapped around parts of the tilt posts 3, 3' (hereinafter it is called as a tape loading angle) is much greater than the angle through which the tape is wound around the single tilt post of the U-type loading system. This is because the tape 15 travels to the tilt post 2 on the tape entrance side, with its upper edge positioned parallel with the surface 17, then has its travelling direction abruptly changed by the tilt post 3, then is smoothly guided onto the tape contact point "m" of the cylinder 1 which is inclined to the surface 17 at an angle .alpha., about twice the read angle .delta.; the tape 15 further travels toward the tape release point "n" of cylinder 1, with its upper edge inclined to the surface 17, has its traveling direction suddenly changed by the other tilt post 3' set on the tape exit side, and finally travels, with its upper edge rendered parallel with the surface 17 of the chassis.
With an 8 mm VTR, the tape loading angle of the rotary head cylinder 1 is standardized to 221.degree. regardless of the kinds of the tape loading systems. And in the 8 mm VTR using the parallel loading system, the cylinder 1 was inclined at 12.degree. to the surface 17 of the chassis, the same angle as observed in the 12.7 mm VTR. Then, the sum of the tape loading angles of the tilt posts 3, 3' was found to be about 140.degree. , as calculated by the present inventor.
Therefore, a considerably large frictional force is produced between the magnetic recording tape 15 and each of the tilt posts 3 and 3' and considerable tension is imported to the tape 15. When a thin magnetic recording tape in which a magnetic layer is formed by a metalization (hereinafter, it is called as a metalized magnetic tape) is used, frictional resistance is further increased. This is because its adhesivity to the peripheral surface of the rotary head cylinder 1 and the tilt posts 3, 3' is far greater than that of the tape 15 in which a magnetic layer is formed by a pasting process. As a result, the metalized magnetic tape is liable to be damaged and an irregular running.
The U-type loading system, which is as commonly used as the parallel loading system, has a merit and a drawback which are diametrically opposite to those of the parallel loading system. More specifically, it is advantageous in that the tape encounters little frictional resistance, regardless of its width; is disadvantageous in that the VTR using it is far larger and thicker than the VTR using the parallel loading system. Obviously, the U-type loading system is less desirable than the parallel loading system in the field of the 8 mm VTR which is expected to be made portable. Nevertheless, when a recording tape with a thermally deposited magnetic layer is used, it is considered far more advantageous than the parallel loading tystem. Hence, the manufactures of VTRs are trying to make the U-type loading system more adapted for the 8 mm VTR. The Japanese Patent Disclosure (Kokai) 57-21265 discloses a modified, simple-structured U-type loading system. This U-type loading system is known as "a .mu.-type loading system" to the people skilled in the art.
FIGS. 4 and 5 show a plan view and partially sectional side views of the .mu.-type loading system, respectively. In these figures, the same reference numerals are used to denote like or the same elements as shown in FIGS. 1 to 3. A detailed description of the like or same elements will be omitted.
In the .mu.-type loading system, a magnetic recording tape 15 is pulled out of a cassette 16 by first to third guide rollers 22, 23 and 24 and a tilt post 25 which is not rotatable. The guide rollers 22, 23, 24 and tilt post 25 are mounted on a loading ring 21 which may rotate clockwise around a rotary head cylinder 1. The tape 15 is then wound around the cylinder 1. Unlike in the case of the parallel loading system, the rotary head cylinder 1 is inclined in a direction (shown by arrow S) opposite to the direction in which the tape 15 is moved away from the cylinder 1. A tilt angle .alpha. is set to be about 5.degree. and is substantially the same as a read angle with respect to the tape 15. Therefore, as shown in FIG. 5, the upper edge of the tape 15 fed from the cylinder 1 to a capstan 12 is substantially parallel to the chassis surface 17 of the video tape recorder. For this reason, the .mu.-type loading system need not be provided with a member equivalent to the tilt post 3' which is indispensable to the parallel loading system and which is disposed on the tape exit side to compensate the inclination of the upper edge of the tape 15 to the chassis surface 17 in the parallel loading system. The omission of the tilt post 3', which is a fixed post with the large tape loading angle (i.e., about 70.degree. ) and which imposes a large frictional force on the tape 15, decreases the frictional force acting on the magnetic recording tape 15.
Furthermore, when the .mu.-type loading system is applied to the 8 mm VTR in which the tape loading angle of the rotary head cylinder 1 is 221.degree. , it is most desired, as the inventor has calculated, that the tape loading angle of the tilt post 25 be about 30.degree. . Apparently, the frictional resistance imposed on the tape 15 is far less than in the case of the parallel loading system. Furthermore, since the guide posts 27 and 26 are fixed on the chassis surface 17 of the video tape recorder in the vicinity of a tape exit point "n" and a tape entrance point "m" of the rotary head cylinder 1, the magnetic recording tape 15 may travel stably at all times. Therefore, even if a thin magnetic recording tape with a thin magnetic layer metalized thereon is used, it will not be damaged or unstably travel.
Indeed the .mu.-type loading system is simpler in structure than the U-type loading system, but it cannot help reduce the planar size or thickness of the video tape recorder. This is because the .mu.-type loading system is essentially identical with the U-type loading system in respect of the method of winding the tape around the rotary head cylinder 1.
More specifially, as shown in FIG. 5, the cylinder 1 is inclined in the direction of arrow S so that the upper edge of the tape 15 may travel from the cylinder 1 to the capstan 12, parallel to the upper surface 17 of the chassis. If the tape 15 could not travel in this way, a tilt post should be provided in the vicinity of the tape exit point "n" of the cylinder 1. Since the rotary head cylinder 1 is inclined in the direction of arrow S, the first guide roller 22 is inclined toward the tape entrance point "m", as shown in FIG. 4. Otherwise, the tape 15 may not be smoothly guided to the tape entrance point "m" of the cylinder 1. Moreover, to minimize the frictional resistance to the tape 15, the first guide roller 22 is made to rotate freely. Hence, the tape 15 may move on this roller 22 along the axis thereof, thus causing a track displacement. To avoid a track displacement, the upper longitudinal edge of the tape 15 at the first guide roller 22 is set at height h from the upper surface 17 of the chassis, which is greater than the height H of the upper longitudinal edge of the tape 15 at the tape exit point "n" of the rotatry head cylinder 1. In other words, that portion of the tape 15 which travels from the guide roller 22 to the tape entrance point "n" is inclined. Since the tape 15 is so inclined, the .mu.-type loading system is inevitably thicker than the parallel loading system. The 8 mm VTR with the .mu.-type loading system cannot be as thin as desired.
The tape loading angle of the tilt post 25 is only 30.degree. in order to reduce the frictional resistance which the tape 15 may receive from the post 25. Therefore, the distance L.sub.2 between the tilt post 25 and the first guide roller 22 must be relatively long so as to increase the height of the upper longitudinal edge of the tape 15 from "H" to "h" as the tape 15 runs from the tilt post 25 to the first guide roller 22 through the distance L.sub.2. The planar size of the 8 mm VTR with the .mu.-type loading system is inevitably greater than that of the 8 mm VTR with the parallel loading system.
Suppose the .mu.-type loading system is used in an 8 mm VTR in which the tape loading angle .beta. and read angle .delta. are standardized as 221.degree. and about 5.degree., respectively. Since an erasing head 9, which has a width of 8 mm, is disposed between the tape entrance point "m" and the first guide roller 22, the distance L.sub.1 between the "m" and the roller 22 is so set that it is about 28 mm. In this case, height "h" is greater by about 12 mm than height "H". As mentioned above, the tape loading angle of the tilt post 25 is about 30.degree. . Hence, distance L.sub.2 is calculated to be 74 mm. It follows that the loading ring 21, on which the first to third guide rollers 22, 23, 24 and the tilt post 25 (unrotatable) are mounted, must have a diameter of approximately 90 mm.
Further, if the erase head 9 is removed, thus reducing the distance L.sub.1 to 20 mm, while leaving the other dimensional conditions unchanged, height h is greater by 11 mm than height H, as calculated by the present inventor.